Please help!Intermittent Immobiliser fault

I have a W Reg Audi A6 1800T. I bought it 2 years ago and it has an intermittent immobiliser fault. Sometimes when I try to start the engine it turns over and dies and the immobiliser light flashes. Sometimes it starts after about 6 attempts but sometimes it doesn't start at all. To make matters worse, every time i get a Recovery truck to take it to the dealer it starts first time when i get there!!
I have had a new reader coil fitted and a dummy ignition box with all keys recoded and it still does it. the local Audi dealer had it in for 2 days and said that they even put faults into the sytem so that they could cancel them out to see if this would help - it didn't!
I recently had to be towed to the dealer, at their request,as they can never find any fault registered when it is working. WE finally reached the dealership and the immobiliser light suddenly stopped flashing an dthe engine started first time. Unbelievable! Can anyone please help me?

Not wanting to teach grandmama egg sucking, but are you sure it's the immobiliser?

From the excellent site UsedCarExpert.co.uk:

If the car won't start, hold the accelerator down to the floor and turn the key. Hold the key down and let the engine turn over. After a few turns, the car will usually start.

These cars often won't start because when it was last moved, it was started, moved a short distance and then stopped. This fills the engine with fuel.

THanks for that but it happens after i have been parked after both long and short journeys. Do you think that this may be why it starts after it has been towed for a while?

I have a similar intermittent failure to start on my 1999 1.9 TDi A6 (exact same symptoms), and I think it is a break in the wiring loom from the key pickup coil (which you had replaced), where the loom allows the angle of the column to be raised or lowered. Mine is so intermittent that I haven't done anything more than move the wiring loom around a little.

Identical problem on 1998 TDi A4. That annoying key light doesn't go off. Which cuts off the fuel supply and hence doesn't let the engine run for more than a second or so.

Its been doing it for years. Dealership want £117/hour evaluation costs, so I will try your wiring loom wiggle trick. Thanks for that.

Is it possible to disable the immobiliser using the OBD link, my car is not worth stealing and this problem is annoying.

Matt

Please see response from Undercover about turning the key etc. This ahs worked for me every time since he told me.

I have a MK4 Golf 110 Gt Tdi.
I was having the same trouble.Had a fault diagnostic done and found none. I read somewhere (maybe on here) that this problem had been solved by putting the key in and the ignition on.
Leaving it on until the immobiliser light went out, about ten mins in my case.
Turned the ignition off and then started the car as normal.
No trouble since.